KABUL, Afghanistan (CNN) -- A car bomber targeted a U.S. base in eastern Afghanistan, killing seven people Wednesday, a day after Taliban militants attacked many locations in the city of Khost, U.S. military officials said.

A U.S. soldier on patrol in Khost province in February 2009.

The suicide bomber drove his vehicle near the entrance of Camp Salerno, near Khost, on Wednesday morning. The explosion killed mostly Afghan civilians and injured 21 others, law enforcement said.

Authorities had no information about whether there were U.S. casualties.

U.S. military and local officials also reported fighting in the southeastern province of Paktika on Tuesday morning.

Taliban fighters attacked Afghan security forces, and U.S. forces joined the battle. Six Taliban fighters and two civilians were killed.

Also on Tuesday, a Taliban suicide bomb squad disguised as regular Afghan army troops stormed the strategic city of Khost, close to the border with Pakistan Tuesday, prompting a fierce six-hour battle with U.S. troops, local officials and the U.S. military said.

The insurgents attacked a municipal building in the center of the city, a U.S. military spokesman said. At least 10 suicide bombers were killed in the attacks, which also left five troops and four civilians dead, Afghan police said.

Local police chief Abdul Qayum Baqee Zoi told CNN the attacks, which ended at 4:30 p.m. involved 10 Taliban suicide bombers in Afghan National Army uniforms and explosive vests. Seven detonated and three were shot dead.

A U.S. military spokesman said the city -- a hotbed of Taliban activity --remained volatile as reports of running battles, kidnappings and fatalities surfaced.

The developments came shortly after the United States announced it was changing its military leadership in Afghanistan, replacing Gen. David McKiernan with Lt. Gen. Stanley McChrystal, a former special operations chief.

Tuesday's fighting began when U.S. forces responded to a suicide bomber at a government compound in the city and came under heavy attack, the U.S. military spokesman said.

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Officials in Khost told CNN that insurgents attacked the municipal building, and the police chief there said attackers killed two police officers, two security guards and two civilians in that incident.

A Taliban spokesman in Afghanistan earlier told CNN 30 Taliban fighters were involved in the attack, and confirmed they were suicide bombers wearing explosive vests.

The U.S. military spokesman said U.S. troops killed several militants but had to fall back.

A U.S. quick reaction force from a nearby base was called in, entering the city with U.S. ground forces, he said.